detection is much more difficult, since there is no unambiguous way to locally detect after a timestep whether a cloth node which has penetrated is on the "wrong" side or not. Solutions involve either using the history of the cloth motion to determine if an intersection event has occurred, or doing a global analysis of the cloth state to detect and resolve self-intersections. Pixar has presented a method which uses a global topological analysis of mesh intersections in configuration space to detect and resolve self-interpenetration of cloth. Currently, this is generally too computationally expensive for real-time cloth systems. To do collision detection efficiently, primitives which are certainly not colliding must be identified as soon as possible and discarded from consideration to avoid wasting time. To do this, some form of spatial subdivision scheme is essential, to avoid a brute force test of primitive collisions. Approaches used include: Bounding volume hierarchies (AABB trees, OBB trees, sphere trees) Grids, either uniform (using hashing for memory efficiency) or hierarchical (e.g. Octree, kd-tree) Coherence-exploiting schemes, such as sweep and prune with insertion sort, or tree-tree collisions with front tracking. Hybrid methods involving a combination of various of these schemes, e.g. a coarse AABB tree plus sweep-and-prune with coherence between colliding leaves. Other applications Other effects which may be simulated via the methods of soft-body dynamics are: Destructible materials: fracture of brittle solids, cutting of soft bodies, and tearing of cloth. The finite element method is especially suited to modelling fracture as it includes a realistic model of the distribution of internal stresses in the material, which physically is what determines when fracture occurs, according to fracture mechanics. Plasticity (permanent deformation) and melting Simulated hair, fur, and feathers Simulated organs for biomedical applications Simulating fluids in the context of computer graphics would not normally be considered soft-body dynamics, which is usually restricted to mean simulation of materials which have a tendency to retain their shape and form. In contrast, a fluid assumes the shape of whatever vessel contains it, as the particles are bound together by relatively weak forces. Software supporting soft body physics Simulation engines Games See also Deformable body Rigid body dynamics Cloth modeling Breast physics References External links "The Animation of Natural Phenomena", CMU course on physically based animation, including deformable bodies Soft body dynamics video example Introductory article Article by Thomas Jakobsen which explains the basics of the PBD method Classical